通過上節的筆記,瞭解到Service的調用方式有兩種,其中使用startService的方式很好理解,就像是啓動一個Activity一樣,只不過沒有UI界面,這節主要記錄使用bindService()的方法,通過實例能更好的掌握使用方法
綁定的Service通過一個客戶端和服務端的接口(這裏客戶端指要進行綁定的其他組件,服務端指這個Service),允許其他組件通過綁定,向Service發送請求,接收回應。綁定的Service完全依附與和它綁定的組件,也就是說他們的生命週期是相關的,當綁定它的組件銷燬時,Service也就銷燬了
一個Service可以同時被啓動(通過startService())和被綁定(通過bindService())如果綁定了一個通過啓動方式調用的Service,那麼在解綁後,這個Service不會被銷燬,除非調用stopSelf()或者stopService(),也就是說綁定並不能影響一個啓動的Service的生命週期;
使用綁定的Service的方式:
- 通過繼承Binder類:(大多數時候使用這種方式)適用於Service只在當前應用程序中,並且與其他組件在同一個進程中運行,下面是一個使用這種方法的例子
首先是Service中的代碼:
public class LocalService extends Service {
// Binder given to clients
private final IBinder mBinder = new LocalBinder();
// Random number generator
private final Random mGenerator = new Random();
/**
* Class used for the client Binder. Because we know this service always
* runs in the same process as its clients, we don't need to deal with IPC.
*/
public class LocalBinder extends Binder {
LocalService getService() {
// Return this instance of LocalService so clients can call public methods
return LocalService.this;
}
}
@Override
public IBinder onBind(Intent intent) {
return mBinder;
}
/** method for clients */
public int getRandomNumber() {
return mGenerator.nextInt(100);
}
}
然後是客戶端的代碼:
public class BindingActivity extends Activity {
LocalService mService;
boolean mBound = false;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
}
@Override
protected void onStart() {
super.onStart();
// Bind to LocalService
Intent intent = new Intent(this, LocalService.class);
bindService(intent, mConnection, Context.BIND_AUTO_CREATE);
}
@Override
protected void onStop() {
super.onStop();
// Unbind from the service
if (mBound) {
unbindService(mConnection);
mBound = false;
}
}
/** Called when a button is clicked (the button in the layout file attaches to
* this method with the android:onClick attribute) */
public void onButtonClick(View v) {
if (mBound) {
// Call a method from the LocalService.
// However, if this call were something that might hang, then this request should
// occur in a separate thread to avoid slowing down the activity performance.
int num = mService.getRandomNumber();
Toast.makeText(this, "number: " + num, Toast.LENGTH_SHORT).show();
}
}
/** Defines callbacks for service binding, passed to bindService() */
private ServiceConnection mConnection = new ServiceConnection() {
@Override
public void onServiceConnected(ComponentName className,
IBinder service) {
// We've bound to LocalService, cast the IBinder and get LocalService instance
LocalBinder binder = (LocalBinder) service;
mService = binder.getService();
mBound = true;
}
@Override
public void onServiceDisconnected(ComponentName arg0) {
mBound = false;
}
};
}
注:上面的例子中沒有解綁Service,一般是需要解綁(unbind)的
- 使用Messenger:如果需要和其他線程通信,就需要用到Messenger,下面是例子
首先是Service的代碼:
public class MessengerService extends Service {
/** Command to the service to display a message */
static final int MSG_SAY_HELLO = 1;
/**
* Handler of incoming messages from clients.
*/
class IncomingHandler extends Handler {
@Override
public void handleMessage(Message msg) {
switch (msg.what) {
case MSG_SAY_HELLO:
Toast.makeText(getApplicationContext(), "hello!", Toast.LENGTH_SHORT).show();
break;
default:
super.handleMessage(msg);
}
}
}
/**
* Target we publish for clients to send messages to IncomingHandler.
*/
final Messenger mMessenger = new Messenger(new IncomingHandler());
/**
* When binding to the service, we return an interface to our messenger
* for sending messages to the service.
*/
@Override
public IBinder onBind(Intent intent) {
Toast.makeText(getApplicationContext(), "binding", Toast.LENGTH_SHORT).show();
return mMessenger.getBinder();
}
}
然後是客戶端的代碼:
public class ActivityMessenger extends Activity {
/** Messenger for communicating with the service. */
Messenger mService = null;
/** Flag indicating whether we have called bind on the service. */
boolean mBound;
/**
* Class for interacting with the main interface of the service.
*/
private ServiceConnection mConnection = new ServiceConnection() {
public void onServiceConnected(ComponentName className, IBinder service) {
// This is called when the connection with the service has been
// established, giving us the object we can use to
// interact with the service. We are communicating with the
// service using a Messenger, so here we get a client-side
// representation of that from the raw IBinder object.
mService = new Messenger(service);
mBound = true;
}
public void onServiceDisconnected(ComponentName className) {
// This is called when the connection with the service has been
// unexpectedly disconnected -- that is, its process crashed.
mService = null;
mBound = false;
}
};
public void sayHello(View v) {
if (!mBound) return;
// Create and send a message to the service, using a supported 'what' value
Message msg = Message.obtain(null, MessengerService.MSG_SAY_HELLO, 0, 0);
try {
mService.send(msg);
} catch (RemoteException e) {
e.printStackTrace();
}
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
}
@Override
protected void onStart() {
super.onStart();
// Bind to the service
bindService(new Intent(this, MessengerService.class), mConnection,
Context.BIND_AUTO_CREATE);
}
@Override
protected void onStop() {
super.onStop();
// Unbind from the service
if (mBound) {
unbindService(mConnection);
mBound = false;
}
}
}
綁定的Service的生命週期:
如下圖